Some opponents of various biotechnologies-particularly genetically modified foods-have a tendency, even when they could be citing scientific and economic studies that back their position, to fall back on the "yuck factor." Illustrations of snarling anthropomorphic cornstalks tend to grab one's attention faster than carefully written arguments in a magazine. It may work, but vague queasiness and discomfort with the unfamiliar are hardly the recipe for an educated opinion.

In discussions about bioengineered animals, the yuck factor is alive and well. (Pigs that glow in the dark? Gross!) So too, however, is its counterpart, one less common in discourse on GM crops: the "cool factor." As Paul Root Wolpe points out, it's easier to latch onto an individual case, and a number of individual animals have gained fame-or infamy-for their bioengineering, with nicknames to boot. Our cast of characters includes:

"Dolly": The first cloned sheep.

"The Beltsville pigs": Seventeen pigs developed to express extra growth hormones, but suffered an array of ailments as a result and became an icon for animal welfare activists.

"The Vacanti Mouse": Lab mouse with what looked like a human ear (actually shaped cow cartilage) on its back.

"ANDi": Lab monkey genetically altered with a jellyfish gene, to make it glow.

"Enviropig": Developed to have reduced phosphorous levels in its manure.

"Popeye pigs": Purportedly healthier pigs as a result of an introduced spinach gene which lowered levels of saturated fat.

Whatever the researchers' intentions, the projects that make the news are often those which can most easily be framed in an attention-grabbing way. The New Scientist dubs bioengineered animals "creatures with bonus features," and various websites and blogs have posted their lists of the "top ten coolest" or "most bizarre genetically modified animals." In some bioengineered animals, pets in particular, "coolness" is actually their primary utility. GloFish (the name is self-explanatory) are marketed specifically as pets, were granted approval for sale in the U.S., and have already spawned imitators-although their original intended use was as a warning system for pollution levels in water.

It's easy to get distracted by the bizarre bioengineered animals, but the majority of the most important ones don't glow under a UV light. "Knockout mice," engineered not to express a certain gene, are a lab standby and could lead to "knockout monkeys." Genetically modified salmon look just like regular salmon, only larger, but they pose very real risks to natural fisheries and ocean ecosystems. Pigs modified to be human organ donors are certainly bizarre in concept, but on the outside they still look like pigs.

Bioengineered animals are a strange lot, to be sure; but within that lot, as far as the impact a modified animal may have on the human and natural world, the book can rarely be judged by its cover.